NEW HAVEN >> This seagoing arthropod that was an ancestor of the lobster grew to be almost 6 feet long.

It’s known as Pentecopterus, named for Greek warships called penteconters, and its fossil was discovered recently in Iowa, where it swam 467 million years ago during the Palaeozoic Period, according to a Yale University release.

It does bear a resemblance to the 50-oared galley ships, featuring a head shield, a slim body and large legs. It’s the oldest described eurypterid and will be featured in the Sept. 1 online edition of the journal BMC Evolutionary Biology, according to the release.

“This shows that eurypterids evolved some 10 million years earlier than we thought, and the relationship of the new animal to other eurypterids shows that they must have been very diverse during this early time of their evolution, even though they are very rare in the fossil record,” said James Lamsdell, a post-doctoral associate at Yale University and lead author of the published study.

“Pentecopterus is large and predatory, and eurypterids must have been important predators in these early Palaeozoic ecosystems,” Lamsdell said. In addition to lobsters, its descendants include spiders and ticks.

The Pentecopterus fossils were found in a meteorite crater near the Upper Iowa River by geologists working with the Iowa Geological Survey. The river was temporarily dammed in 2010 to expose the fossils, which include well preserved juveniles and adults so researchers are able to study the creature’s development, the release said.

“The Winneshiek site is an extraordinary discovery,” said Yale paleontologist Derek Briggs, curator of invertebrate paleontology at the Yale Peabody Museum of Natural History and a co-author of the study. “The fossils are preserved in fine deposits of sediments where the sea flooded a meteorite impact crater just over 5 kilometers in diameter.”

Huaibao Liu of the Iowa Geological Survey and the University of Iowa, who led the fossil dig and is a co-author, said, “The undisturbed, oxygen-poor bottom waters within the meteorite crater led to the fossils’ remarkable preservation.”